The present disclosure relates generally to medical devices and, more particularly, to sensors and systems for measuring physiological parameters of a patient.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such characteristics of a patient. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.
In some instances, physicians may wish to have information about the condition and state of internal organs such as the heart. Cardiac activity may be assessed by a variety of methods, including echocardiography, which may be used for measuring stroke force, inotropism, contractility and ejection fraction. In addition, the amount of blood a heart ejects in one heartbeat, stroke volume and other hemodynamic parameters are frequently determined. An additional parameter, cardiac output (i.e., cardiac output per minute) may also be determined. From these parameters, a general determination of cardiac function may be derived, which in turn is a basis for the diagnosis of heart diseases and other clinical conditions.
Because patients in hospital settings may experience sudden changes in heart condition, it may be advantageous to collect cardiac data continuously to more quickly respond to such changes. However, some techniques for determining cardiac function may not be suitable for long-term continuous monitoring of a patient. For example, echocardiography is not really appropriate for monitoring patients with serious heart diseases in ICUs because it involves the constant attention of medical personnel.
One existing technique for determining cardiac function which has been developed is known as impedance cardiography. Impedance cardiography involves measuring the electrical impedance of a subjects body using a series of electrodes placed on the skin surface. Changes in electrical impedance at the body's surface are used to determine changes in tissue volume that are associated with the cardiac cycle, and accordingly, measurements of cardiac output and other cardiac function. Such impedance-based techniques, however, may be relatively inaccurate in calculating certain hemodynamic parameters, such as stroke volume, for certain patients.